1. Field
The invention relates to the field of manufacture of tires, comprising flexible walls arranged in a groove of the tire tread pattern.
2. Description of Related Art
The purpose of the grooves in the tread pattern is to drain away and remove water when the tire is running on wet or soaking wet ground. These grooves are the cause of some of the running noise phenomena in that they constitute regions in which air under pressure accumulates, generating sound waves. The grooves run in the circumferential direction and in the axial direction and their layout, dimensions and the number of them are the subject of detailed study on the part of tire tread pattern designers.
With a view to reducing the level of tire running noise, while at the same time preserving the water clearance qualities, it is known practice in the prior art to position flexible walls of small thickness in a direction transverse to the direction of the grooves. These mobile walls, also known as flaps, have the special feature, like a door, of extending transversely from one of the walls of the groove and of remaining in the closed position when the tire is running on dry ground, so as to block the spread of the sound waves, and of being able to open when the tire is running on wet ground in order to allow the water that enters the drainage groove to be cleared.
Publications FR 2 715 891, GB 2 450 723 or even EP 908 330 describe varying embodiments of these noise-reducing devices.
The noise-reducing devices described in these publications are connected to one of the walls of the groove, and this connection forms a kind of articulation about which the mobile wall of the noise-reducing device, on account of its flexibility, passes successively from the open position into the closed position under the action of the pressure from the water or from the air.
The flexible wall or door may itself have one or more radial cuts. The thickness of the flexible walls varies between 0.2 mm and 1 mm. The width of the cuts can be adjusted at will according to the particular shape that it is wished that the lateral edges of the door of the noise-reducing device should have.
In practice, the moulds intended for moulding the tires comprising these contrivances comprise substantially radial cuts made in the ribs intended to mould the draining grooves, which run transversely to the direction of the said ribs.
However, there are a great many difficulties associated with creating these cuts with the required level of accuracy because of the need to control undercuts. In addition, when a high number of tires is going to be moulded using a mould comprising the said cuts, it is found that the cuts become soiled or even plugged, this being detrimental to the quality of the tire obtained, and dictating the need for extensive and costly maintenance.